1. Field of the Invention
The present invention relates to a lock mechanism in which, by pressing an openable cover of an audio apparatus, an audio-apparatus accommodating case or the like, or an openable member of such as a door of a box or the like, the openable cover or member is engaged with or disengaged from a main body. The present invention also relates to a latch device in which a latch body is retained in a pushed-in state or a withdrawn state in a housing so as to be provided with the same function as that of the lock mechanism.
2. Description of the Related Art
In a typical audio apparatus or the like, a latch device L is provided on an openable cover so as to retain the openable cover, as shown in FIG. 4.
As shown in the drawing, the latch device L is arranged such that each time a latch body 10 is pressed by a striker 34 in the direction of arrow A, a tracing member provided in a housing 14 moves halfway in a heart-shaped circulatory cam groove formed in the latch body 10, thereby allowing the latch body 10 to be retained in the housing 14 alternatively in a state in which the latch body 10 is pushed in and in a state in which it is withdrawn. Concurrently, as shown in FIG. 5, while a pair of arms 50 formed on the latch body 10 are respectively being pressed by a pair of rectangular frames 40 of the housing 14, the striker 34 fixed to the openable cover is clamped or released, thereby setting the openable cover in a closed state or in an openable state.
As shown in FIGS. 4 and 5, each of the arms 50, which are generally provided on the latch body 10, comprises a holder portion 50A for clamping the striker 34 and a hinge portion 50B serving as a center of rotation of the holder portion 50A. The arms 50 are formed of a flexible material such as nylon so as to facilitate the bending of the hinge portions 50B and reduce their frictional resistance with respect to the rectangular frames 40.
However, there has been a drawback in that if a large tensile load (acting in the direction of arrow B in FIG. 5) is continuously applied to the striker 34 while the respective holder portions 50A of the arms 50 are holding the striker 34, since the hinge portions 50A are flexible, the hinge portions 50B become elongated or offset in the direction in which the holder portions 50A are spaced apart from each other, thus causing the striker 34 to come off the holder portions 50A.
To give a more detailed description, when a tensile force W shown in FIG. 5 acts on each holder portion 50A via the striker 34, if the length of the arm is assumed to be L, a bending moment M (M=WL/2) acts on each hinge portion 50B. Accordingly, each hinge portion 50B rotates in the direction in which the holder portions 50A are spaced apart from each other. In addition, since a tensile force .sigma. (.sigma.=M/Z, Z: coefficient of a cross section) due to the bending moment M acts on each hinge portion 50B, the hinge portions 50B become elongated in the direction of arrow B. As a result, the holder portions 50A become offset in the direction of arrow B while becoming spaced apart from each other. Hence, there has been the drawback that the striker 34 is liable to come off the holder portions 50A.
In addition, since an outer side of the hinge portion 50B is formed as a curved portion D, there has been another drawback in that if the tensile force W acts, the curved portion D is pulled, so that the hinge portion 50B becomes elongated.
In a typical latch device such as the one shown in FIG. 14, a rear end portion 182B of a tracing member 182 moving in a circulatory cam groove 180 in a circulatory manner is rotatably inserted in a fitting hole 184 formed in the unillustrated housing. In addition, the tracing member 182 is pressed by a pressing leaf spring 188 secured to the housing by means of a screw 186 such that the tracing member 182 will not come out of the fixing hole 184.
However, with the above-described structure for fitting the tracing member 182, the tracing member 182 cannot be fit in the housing from the outside thereof. For this reason, it has been necessary to fixedly hold the tracing member in the housing in advance, and then to allow a tip portion 182A of the tracing member 182 to be fitted into the circulatory cam groove 180 formed in a latch body 190 which is inserted into the rear portion of the housing.
For this reason, in the event that the tip portion 182A of the tracing member 182 is shaken during the assembling operation, the tip portion 182A cannot be inserted into the circulatory cam groove 180, and the tip portion 182A of the tracing member 182 is brought into contact with a different portion of the latch body 190. Hence, a drawback has been encountered in that the latch body 190 cannot be inserted into the housing, so that the assembling of the latch device has been troublesome. In addition, a pressing member (e.g., a pressing leaf spring 188) is required for pressing the tracing member 182, with the result that the number of component parts used disadvantageously increases and the assembling efficiency has been low.
Meanwhile, in a center cluster portion of an automobile, a push-open type ash pan is provided which automatically slides out upon pressing of its cover.
This push-open type ash pan is provided with a lock mechanism 280 as shown in FIG. 30. This lock mechanism 280 operates as follows: If a front face portion of the unillustrated ash pan is pushed in the direction of arrow R, a tracing member 284 fixed to a rear end portion of the ash pan is inserted into a heart-shaped circulatory cam groove 282 formed in a box. The inserted tracing member 284, when thus pressed, moves in the heart-shaped circulatory cam groove 282 in a circulating manner, and when the tracing member 284 engages a recessed (cusp) portion 292 of the heart-shaped circulatory cam groove 282, the tracing member 284 retains the ash pan in a state in which the ash pan is pushed in.
In the lock mechanism 280 shown in FIGS. 30 and 31, a stepped portion 288 is provided so that the tracing member 284 can circulate in a set direction (in the direction of arrow Q) in the circulatory cam groove 282, so as to prevent the tracing member 284 from circulating in an opposite direction. In addition, an urging means 290 is provided separately for urging a tip portion 286 of the tracing member 284 vertically toward the bottom surface of the circulatory cam groove 282 to ensure that the tracing member 284 will circulate with its tip portion 286 brought positively into sliding contact with the bottom surface of the circulatory cam groove 282.
With the mechanism in which the tip portion 286 of the tracing member 284 is caused to slide on the bottom surface of the circulatory cam groove 282, a shortcoming has been experienced in that, owing to the friction of the bottom surface of the groove with the tip portion 286 of the tracing member 284, the circulatory cam groove 282 sometimes becomes worn or deformed, and the stepped portion 288 is scraped off, thereby causing the tracing member 284 to circulate in the opposite direction.
In the state in which the ash pan is pushed in, the tracing member 284 is retained at the recessed portion 292 formed in the circulatory cam groove 282, and the state in which the ash pan is pushed in is maintained against the urging force of an unillustrated compression coil spring. However, since the urging force of the compression coil spring is supported at one recessed portion 292, the recessed portion 292 is liable to become damaged. Hence, the rupture strength of the lock mechanism 280 has been low.
In addition, since the tip portion 286 of the tracing member 284 is urged towards the bottom surface of the circulatory cam groove 282, there is a need to provide the urging means 290 separately, so that the number of component parts used disadvantageously increases and the assembling efficiency has been low.
Although the tracing member 284 is usually formed of a metal material into the shape of a lever, there have been cases where if fabrication accuracy at the time of its formation is poor, the tracing member 284 scrapes off the bottom surface of the circulatory cam groove 282, or the tracing member 284 undergoes deformation due to its frictional resistance with respect to the circulatory cam groove 282.
In the case of a latch device employing the above-described lock mechanism 280, since it is necessary to form the stepped portion 288 in the circulatory cam groove 282 provided in the latch body, and to provide the tracing member 284 with the urging means 290, the housing which accommodates the latch body and the tracing member is required to have a minimum thickness. For this reason, it has been difficult to make the latch device thin beyond this restriction.